1. Field of the Invention
This invention relates to the mechanical arts. In particular, it relates to a slidable duct assembly for use in aircraft anti-icing conduit systems.
2. Discussion of the Related Art
As is well-known, jet aircraft engines provide the thrust needed to propel jet aircraft. Additionally, by redirecting a portion of the compressed, bleed air produced by the engines through a conduit system, the air can be used for a variety of other purposes. These other purposes include pressurizing, heating, and cooling the aircraft's cabin, and removing moisture from its front windows. To be effective, the conduit system must not only minimize the escape of the bleed air, but it must withstand the elevated temperatures, often in excess of 650.degree. F., of the bleed air produced by today's jet aircraft.
Another important use for the bleed air is to de-ice the aircraft wings' leading edges, wing slats and elevons. For example, to de-ice the movable slats located on the leading edge of the aircraft wings, hot, compressed, bleed air is transferred through conduit sections from a supply duct running lengthwise in the wings' leading edge to a spray duct running lengthwise in the wings' slats. The spray duct has openings to deliver the bleed air to the interior surface of the slats.
Special considerations are involved in the anti-icing conduit systems used to de-ice movable portions of the aircraft, such as wing slats and elevons, that must undergo a wide range of motions as they are extended and then retracted. In order to track the movement of these components, the conduit system must contain at least two slidable and rotatable conduit sections. Conventional duct assemblies are formed from metallic, tubular, telescoping conduit sections. To maintain the air pressure within the assembly, each conduit section is sealed with an elastomeric seal. It is a drawback of such seals, that they become unstable, if the telescoping conduit sections extend and retract relatively long distances. To overcome this drawback, slide bearings must be provided to give the necessary stability to the duct assembly and to extend the seals' lives.
It is a further drawback of such duct assemblies that the seals electrically insulate the metallic, telescoping conduit sections. This creates the danger of arcing due to static buildup or lightning, thus creating a possible ignition source in the area of the aircraft's fuel storage and distribution systems. Attempts have been made to overcome this problem by the use of flexible wire or cable loops to attach the movable components to the fixed components and provide electrical bonding. A difficulty with the use of flexible wire or cable loops, however, is they can interfere with the extension and retraction of the movable components. Furthermore, they are subject to premature failure because of fatigue.
Accordingly, there has existed a definite need for an improved slidable duct assembly which minimizes the escape of compressed air and is stable at high temperatures, while telescoping over relatively long distances. There has existed a still further need for a slidable duct assembly that is electrically bonded without the use of cumbersome and failure-prone wires or cable loops. The present invention satisfies these and other needs and provides further related advantages.